Pulleys are often used to hoist and/or lower loads in connection with a rope or cable, as generally known in the art. A pulley typically comprises a wheel or sheave that turns on an axis. When used in connection with a rope, a pulley can be used to change the direction of a tension force placed on the rope.
Pulleys are used in several configurations and for various purposes. One example is a block and tackle arrangement in which two pulleys work in unison, one pulley being fixed and another free to move with the load. This simple device may be used to create a mechanical advantage, wherein the tension force required to lift a load is decreased by a factor of two or more, in exchange for a decrease in the speed at which the load ascends. Some sophisticated examples of modern block and tackle arrangements use pulleys in combination with braking and/or clutch devices.
In general, block and tackle systems often require a significant amount of time to prepare for use. The time and effort spent in arranging the elements of a block and tackle system are problematic where the location of the load is remote or where the need to move a load becomes urgent. One example in which a block and tackle arrangement is often impractical is a rescue situation. For example, it is not practical to arrange a block and tackle system where a person has been injured while working in an elevated space, such as where a person has lost consciousness while working on a power line and remains suspended from the power pole.
As an example of the prior art, U.S. Pat. No. 4,220,315 discloses a pulley having an auxiliary braking system, enabling the operator (e.g., rescue personnel) to quickly assemble the device and lower the injured person in a short amount of time. The auxiliary braking system of the prior art comprises a spindle in a chamber, the path of the rope through the chamber comprises a loop of greater than 180°. The load bearing portion of the rope is suspended directly from the sheave, while the operator controls the rope entering the chamber of the auxiliary braking system. The spindle is arranged such that the axis of the spindle may move laterally within the chamber, enabling the operator to control the braking function, in part, by manipulating the angle of the rope entering the chamber.
Disadvantages of this and other existing solutions include that the braking system of currently available devices must frequently be operated from below the device. Further, the amount of complexity involved in arranging the rope in an auxiliary braking system remains high for an operator in view of the expected stress of a rescue effort.